1. Field of the Invention
The present invention relates to a continuously variable gear device for converting a rotary motion into a linear motion which is dependent on the angle of rotation.
2. Discussion of Related Art
For some purposes, gear devices are necessary for changing a rotary input motion into a linearly proportional output motion, i.e. a straight-line movement, wherein the transmission ratio of the device is continuously variable with respect to the rotary input motion.
According to the known state of the art, this object can be achieved by connecting the rotary motion, for example, to a stepped gear device, the output end of which is connected to a continuously variable transmission. The transmission has a range which covers the stepwise progression of the first gear device and thus linearizes the output motion.
When producing electrophotographic copies from microfilms, i.e. in the field of microfilm re-enlargement, the photoconductor web onto which the enlarged film images are reproduced slit-wise has a given operating speed. It is necessary to produce a corresponding, slower linear scanning speed for the microfilm aperture card, which is to be used for projection, by means of a rotary transfer. The linear scanning speed should be slower than the operating speed of the photoconductor web by a factor ranging from 6 to 36, particularly from 7.4 to 29.6. It is obvious that, in the re-enlargement of microfilms, the accuracy of transfer is affected by the number and quality of transfer elements used to convert the rotary speed into a linear output speed. This is particularly true since inaccuracies of the individual transfer elements may accumulate in practice and cause maximum deviations which, in total, exceed the admissible tolerance limit. It may thus occur that the resulting transmission ratio yields microfilm re-enlargements which cannot be satisfactorily reproduced. By means of the stepped gear devices which can be used in the field of microfilm re-enlargement, a stepped transmission of re-enlargement factors is effected by appropriately choosing pairs of gear wheels, so that re-enlargements corresponding to standard format series, for example DIN sizes, are obtained. Owing to the precision required of the gear-wheel pairs used, such stepped transmission gears are very expensive.
Stepped transmission gears of this kind can be constructed according to the prior art, as described, for example, in "Getriebebeispiel-Atlas" (Atlas of Gear-Unit Examples), K. Hain, VDI-Verlag, Duesseldorf, 1973. These stepped transmission gears allow the production of re-enlargements which correspond to given format series. The methods of converting a rotary motion into a linear motion described in this atlas are very complicated and meet, at the most, two of the three aforementioned requirements. Also in the constructions according to which the straight-line output motion is continuously variable, it appears that the transmission ratio cannot be maintained with mathematical accuracy along the entire operating path, i.e. the proportionality factor between the input and output motions changes.